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Thursday, August 12, 2010

Now that I've gotten back from driving through a low desert locality with huge mountains on the western side of the valley, and then driving across central Nevada on one of the dustiest roads in existence, we can return to the trip to Oregon that MOH and I took last month. Where were we? Oh yeah, we had traveled from Jarbidge, NV, to Baker City, OR, on various backroads and I-84.

The morning after attending Barley Brown's Brew Pub, we awoke in our strange motel room (Google Maps), and after checking out the okay but crowded coffee and continental breakfast, we opted for some real coffee and walked downtown to a small cafe that had espresso (Google Maps). We sat outside and enjoyed the view of the brightly colored town of Baker City.Eventually we packed our stuff into the Prius, bought more ice for the Ruby Mountain beer in our ice chest, and headed down Oregon Route 7 toward U.S. Route 26, which we joined at Austin Junction. Between Austin Junction and Prairie City, we crossed over a small part of the famed Blue Mountains. The Blue Mountains are high, cool, and covered with a mixed conifer forest, species of which include one of my favorite tree, the larch. Just west of Dixie Summit, we walked a short trail down to a small section of track that has been laid on the old Sumpter Valley Railroad grade (Google Maps Street View). It's a nice place to take a little break from driving. The third main highlight of the day was coming to the Sheep Rock Unit of the John Day Fossil Beds National Monument, which is mostly north of Highway 26 (MSRMaps, in purple). This national monument comes in three main pieces scattered over eastern Oregon, and the fossils are in several fossil assemblages that range in age from 44 to 7 Ma. I'm not going to get into the palaeontology in any detail, but will to say that the Thomas Condon Paleontology Center has a huge display of ancient flora and fauna including lots of mammal, reptile, and amphibian bones and skulls, and lots plant fossils including nuts and leaves. This first overlook (Google Maps) is of the Mascall Formation, one of the youngest mammal-bearing formations in the park, about 12 to 16 million years old.

The Mascall Formation forms nice badlands of tilted strata overlying flows of the tilted Picture Gorge Basalt (about 16 Ma, in part correlative to basalts seen at Multnomah Falls, and part of the Columbia River Basalt Group). The Mascall is capped by the nearly flat-lying Rattlesnake Tuff, the thin orange-brown unit on the mesa. At first I thought — no, this is Oregon, that must be basalt. I later realized that the Rattlesnake Tuff is a widespread ash-flow tuff unit, often called an ignimbrite at John Day, which erupted 7 million years ago and covered a 30,000 to 40,000 km2 area (as much as 15,000 square miles) of eastern to central Oregon. It's present-day distribution can be seen here. So now, everytime I see a thin, reddish to orangish brown unit amongst a bunch of basalt flows, I wonder... From the Mascall overlook, we looked north along Highway 26 and the John Day River, into Picture Gorge. Just beyond Picture Gorge, you can see a bit of Sheep Rock sticking up, also capped by the 16 Ma Picture Gorge Basalt. We're getting closer: this is the part of Picture Gorge where Rock Creek flows in from the west to join the John Day River flowing north toward Sheep Rock. This is the view of Sheep Rock from the Thomas Condon Paleontology and Visitor Center (Google Maps location). The dark, capping layers are flows of the Picture Gorge Basalt (16 Ma); the central brownish layer is the Picture Gorge Ignimbrite (28.7 Ma). The upper buff to pinkish layers are ashy claystones of the Kimberly Formation (25 to 28 Ma). The lower greenish sediments are ashy claystones of the Turtle Cove Formation (28 to 33 Ma); the green Turtle Cove sediments lie mostly below the Picture Gorge Ignimbrite but also form a thin band above it. The entire section below the capping basalt is part of the John Day Group. A matching photo with some explanations from the Visitor Center (click to enlarge). Zooming in on the Picture Gorge Ignimbrite and the greenish layers below, we can see a fault offsetting the units. The thin white cliffy unit in the middle of the lower section is the Blue Basin Tuff (28.9 Ma). This tuff layer, along with a couple other tuffs and many other sub-units used for correlating different fossil beds, can be see below (click to enlarge). Read more about the stratigraphy and regional geology here. My blathering doesn't really do it justice! The ranger giving an overview of the geology preferred not to use the word fault for the planar-looking structure seen offsetting the units in the previous four photos — and it's called a "minor fault" in displays inside — instead calling it a "crack." I think this was to emphasize that the structure is an old, inactive fault that people shouldn't be afraid of, rather than an "earthquake fault" about to go off at any moment, but possibly he meant it was a growth fault that didn't extend upward through the entire section.

Also, he apparently had to explain constantly that there aren't any dinosaurs at the museum because the fossils are from the Age of Mammals. I guess some people come expecting or hoping to see dinosaurs, but the sediments and tuffs post-date the KT boundary and dinosaurs by about 20 to 60 million years.

It was very hot when we were at John Day Fossil Beds in late July — go early in the morning if it's summer, or wait until fall!So, we left without taking any planned hikes: the road had been long and we still had miles to go — and it was cooler in the Prius. We could follow some of the formations westward toward Redmond, but we finally lost track of whether we were seeing the Rattlesnake Tuff or the same basalts. After settling in at a nice but inexpensive motel in Redmond, we met some Alaskans and joined them for dinner and ale at the Red Dog Depot. I can't really say what kind of IPA was favored, because they changed the available beers almost daily. One was less hoppy than the other; both were less hoppy than the WFO IPA at Barley Brown's in Baker City. The 20" Brown was enjoyed by non-IPA drinkers.

8 comments:

I love this area, though I don't really feel as if I've spent enough time there. I cooked for one of OSU's summer field camps at Mitchell, and was able to go on a couple of the day trips, as well as a few hikes from the camp during on easy days. There are some rock paintings in Picture Gorge (hence the name), but you need to look carefully for them.

Baker City is an, interesting town. I really enjoyed John Day, all 3 units. I constantly get asked about dinosaur fossils even though our youngest rock is 270ma.Sure hope you got in some rockhounding around Prineville. I still have some very nice plume agate from the Crooked River.

I passed through Baker City on my way to Moab in June. Awesome drive on I-84 from Pendleton to Baker City. It was the first time I had passed through this area. I'll make it to Barley Browns someday soon.

DD, I drove on I-84 to Baker City, coming from Portland last fall - don't think I made it to Pendleton - but the part of the road I saw was beautiful, simply because the larch was turning yellow! I don't know much about the geology there, though...